Hydrostatic-machine system

ABSTRACT

A hydrostatic-machine system in which a plurality of hydrostatic machines, e.g., pumps or motors, are connected together in building block or modular relationship by bolting at complementary confronting faces thereof. Each machine has an outer housing of prismatic, preferably cubic, configuration. The faces of the prism, which are not employed for connection with other such machines, are provided with cover plates and/or ports which can be connected with hydrostatic machines of the assembly via ducts attached upon removal of the plates.

D United States Patent 1 51 3,681,919 Fors er 1451 Aug. 8, 1972 [54] HYDROSTATIC-MACHINE SYSTEM 1,433,733 10/1922 Lindsay ..417/238 t 1 F 3,054,263 9/1962 Budzich et a1. ..60/53 A [72] ',j';,f,'5;j camschaf 3,241,317 3/1966 Roeske et a1. ..60/53 A 3,349,860 10/1967 Ross ..60/53 A X [73] Assigneez Linde Aktiehalt, 3,411,296 11/1968 Peterson ..60/53 A Wiesbaden, Germany Primary Examiner-Martin P. Schwadron [22] Flled' Oct. 1970 Assistant Examiner-Leslie J. Payne [21] Appl. No.: 84,766 Attorney-Karl F. Ross 30 Foreign Application Priority um [57] ABSTRACT oct 30 1969 Germany P 19 54 682 8 A hydrostatic-machine system in which a plurality of hydrostatic machines, e.g., pumps or motors, are connected together in building block or modular relationiigd ship by bolting at cqmplemenm confronting faces 58 Field ois eaic iiil6d/s3k62115 11 7/238 239 "E Each machme mum! 4l7l4l7 6 prismatic, preferably cubic, configuration. The faces of the prism, which are not employed for connection with other such machines, are provided with cover [56] References Cited plates and/or ports which can be connected with UNITED STATES PATENTS hydrostatic machinzls tofhthel assembly via ducts att t 2,562,363 7/1951 Nixon ..60/53AX ac e ponremv epaes 3,133,418 5/1964 Froebe...................60/53 A X 15 Claims, 16 Drawing Figures PATENTEDAuc 81972 SHEEI 1 OF 4 Franz Forster INVENTOR.

FIG. 3

Attorney PATENTED 81972 3.681.919

sum ESP 4 mu k S Franz Forster INVENTOR.

FIG. 6

' Attorney PATENTEDAUG 8 I972 SHEET 38F 4 Franz F0 rsfer I N VEN TOR.

rrvnnosmnc-mcmm: SYSTEM FIELD OF THE INVENTION BACKGROUND OF THE lNVENI'ION In the hydraulic field it is known to provide hydraulic pumps and motors for force-transmission purposes. For example, a hydraulic pump may be driven by a prime mover or some other source of motive power and may have its output and input sides connected by a suitable conduit network to one or more hydraulic motors, with or without the intervention of control means in the form of valves. The motor may have an output element which is connected with a load.

in hydrostatic systems the hydrostatic pump and hydrostatic motor are connected in a closed fluid circuit so that the rate of operation of the pump influences the operating parameters of the motor. Such systems are used for the transmission of force with or without alteration in the transmission ratio and the motor and pump are commonly of the axial-piston type. The pump may have an input shaft which rotates a cylinder barrel or otherwise successively displaces a number of pistons extending parallel to one another and generally contained in the cylinder barrel mentioned earlier. On one side of the assembly, fluid is forced by the pistons to the discharge port while fluid enters at the other side of the assembly and is drawn into the individual cylinders. The outlet or discharge port is connected to the intake port of the hydrostatic motor which similarly may have a cylinder barrel with a plurality of pistons bearing against a control surface. Axial-piston pumps and motors have been described at pages 395 if. of SER- VOMECHANISM PRACTICE, McGraw-l-lill Book Company, New York, i960 and are conventional in the art (see FLUID POWER, US. Government Printing Office, [960,pages 109- l l2and l99ff.).

As these publications note, a rotary hydrostatic pump has an input shaft which may be driven while the hydrostatic motor has an output shaft which may drive a load so that a transmission ratio in terms of speed and torque may develop between the input and the output shafts. Hence it is a common practice to associate a hydrostatic pump with a hydrostatic motor in a cornmon installation, such systems being described generically as hydrostatic transmissions. in some cases, it is the practice to provide the hydrostatic motor remote from the hydrostatic pump and to connect the two by relatively long hydraulic lines, although other systems include the motor and pump in a common housing or provide means on the housing of either the pump or the motor for connecting the other hydrostatic machine thereto. The term hydrostatic machine," as used herein, therefore, is intended to designate either a hydrostatic pump or a hydrostatic motor. Incidentally, in many configurations, a hydrostatic pump can be used as a motor and vice versa.

It has been observed that conventional systems for associating hydrostatic machines in groups or assemblies have been inadequate because of the large size of Hydrostatic machines with rotary drives or rotary outputs, operating upon piston principles, also include radial piston pumps, as described, for example, at pages 109 of FLUID POWER. The equivalent radialpiston motors are described at pages 197 ff. of FLUID POWER. Since the invention is applicable to all hydrostatic machines using rotary inputs or outputs, such machines will hereinafter be described as piston-stroke hydrostatic machines.

OBJECT OF THE INVENTION it is, therefore, the principal object of the present invention to provide an improved hydrostatic-machine assembly whereby the aforementioned disadvantages can be obviated.

SUMMARY OF THE INVENTION This object and others which will become apparent hereinafter are attained, in accordance with the present invention, by providing a modular configuration or building-block construction of the piston-stroke machines by providing such machines with complementary, juxtaposable and geometrically similar connecting flanges or faces and constructing the machine housing or exterior in the configuration of a prism. In this case, the machines can be interconnected by bolts or the like in juxtaposition to form an array, row or assembly in which the machines are lined up. The present invention is applicable to hydrostatic piston-stroke machines of a single size or of difierent sizes, it being understood that regardless of the size of the machine, all of the machines of the assembly will have identical connecting flanges or surfaces. The term flange" is used herein to designate a housing surface which is generally planar and can be connected flat against a corresponding surface by bolts or the like, extending transversely to the interface between the machines. The term is not to be considered as necessarily implying a member which projects from another although such projecting members are not excluded in the first instance.

An assembly according to the present invention can include a large pump to which a large motor is joined flange-to-flange, a large pump connected to one or more small motors at corresponding flanges, a pump connectedtootherpumps ofthesamesizeorofsmaller size, or several motors interconnected and tied to a single pump. The terns large" and small" as used herein, together with similar references to size" are intended to designate not only differences in the external dimereions and total volume of the hydrostaticmachines, but also differences in capacity in terms of fluid displacement per rotation. More particularly, I may join a pump with a motor of the same capacity in terms of the stroke volume per revolution, or a motor of larger stroke volume per revolution or another pump, into a single compact assembly. It will be apparent, therefore, that further enclosures for the hydrostatic pump or hydrostatic motor or the assembly are not required, that pedestals and like mounting structures for the hydrostatic machines can be avoided and that the complex connections of prior-art structure can be eliminated.

According to an important feature of the invention, the prismatic housing has a number of faces which lie parallel to or perpendicular to the axis of rotation of the shaft of the machine and which are formed with respective connecting flanges, all of which may be identical. Those flanges which are not employed for connection to another rotary hydrostatic machine, may have an annular recess into which the cover plate fits so that the exterior of the assembly is flush. With multiple connecting flanges, a pump may, for example, be connected selectively with one motor or two motors, or two, three or more pumps may selectively be connected together in a single assembly. Preferably, however, three or more hydrostatic machines are connected together linearly.

It has been found to be most advantageous to provide the external configuration of the hydrostatic machine housing as a parallelopiped, preferably a rectangular parallelopiped with square sides, i.e., of generally cubic configuration. In this case, five connecting flanges may be provided for the machines, the remaining surface serving to clear the shaft. Advantageously, even this surface is formed as a connecting flange according to the principles of the present invention, although it generally will be used to connect the pump to a driving source or a motor to the driven structure.

Thus the flanges lie in planes parallel to the axis of rotation of the shaft or perpendicular thereto, each flange lying approximately at right angles to an adjoining flange of the machine. It is possible, however, to provide one or more flanges of a construction or configuration different from that of the connecting flange for accommodating,for instance, control or regulating devices designed to be mounted upon the housing. To this end, the flanges for the connection of control or regulating devices can be relatively small flanges while the main connecting flanges are geometrically similar but larger. Geometrically identical flanges are preferably provided parallel to one another on opposite sides of the machine so that, for example, the larger flanges lie in a row to enable the machines to be interconnected in a row while the flanges to which the control members are affixed lie perpendicular to these main connecting flanges. It has also been found to be desirable, in some cases, to provide flanges which lie at an angle of, say, 45 to other flanges, thereby permitting other possibilities of connecting the several machines.

At the centers of at least some of the connecting flanges of each machine, fluid ports may be provided for communication upon connection with another machine, thereby eliminating the need for ducts. However, connections may be made between the port flanges by pipes, ducts or the like, terminating in flange covers by which such ducts are bolted to each machine. With a cubic configuration of the housing, it is possible to provide a flange at the end of the machine opposite the driving side which is of a configuration identical to that of the lateral flanges, thereby enabling several machines to be connected in tandem. In this case, the shaft of a hydrostatic pump may be inserted into a socket of another hydrostatic machine to which it is bolted so that rotation of the shah of this other machine also drives the shaft of the first-mentioned machine.

Still another feature of the present invention resides in the provision of mating centering means on the interconnectable flanges, e.g., in the form of an annular recess of each flange into which a ring may be fitted, for proper positioning of the interconnected machines. It is also conceivable to provide a mating centering arrangement whereby a circular ridge is permanently formed in one connecting flange and is receivable in a circular recess in the other. The centering means should also be identical to the centering system provided for the regulating mechanism which may be attached elsewhere upon the housing.

Advantageously, I provide a plurality of bores traversable by bolts and extending through the housing while temrinating at the opposite flanges externally of the aforementioned circular recess. These holes may be located at the vertices of a square i.e., along orthogonal diameters or diagonals of the connecting flange. Threaded bores may be provided along these diagonals within the circular recess to accommodate screws for attaching the cover plates for control mechanisms. The screws traversing the cover plates may be countersunk therein to maintain a flush surface and the floor of the recess may lie in a plane parallel to the plane of the external surface of the flange to form the smaller connecting surface for the control mechanisms. The flanges or one of them may be used for fastening the transmission upon a frame or other support, e.g., the housing of the driven machine or the machine to be driven.

DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is a perspective view of a hydrostatic machine embodying the invention;

FIG. 2 is an elevational view showing this machine connected with a machine of similar size to form a double-pump assembly according to the invention;

FIG. 3 is a view similar to FIG. 2 showing an assembly in which the pumps are of different size;

FIG. 4 is an elevational view of the principles of the present invention as applied to a hydrostatic transmission in which the pump and motor are of the same size;

FIG. 5 is an elevational view showing a similar transmission but with hydrostatic pump and motor of different sizes;

FIG. 6 is an elevational view of a transmission wherein the input and output shafts of the interconnected hydrostatic machines lie in a Z-configuration;

FIG. 7 is an elevational view showing a hydrostatic transmission with two output shafts lying at right angles to the input shafts;

FIG. 8 is an elevational view of a similar transmission wherein, however, the hydrostatic pump and motors are of the same capacity;

FIG. 9 is an elevational view of a right-angle transmission according to the present invention;

FIG. 10 is an elevational view of a Z-type transmission according to another embodiment of the invention;

FIG. 11 is an end view of the transmission showing how some of the connecting flanges may lie in an angle of 45 with respect to other flanges;

FIG. 12 is a diagrammatic elevational view, partly in section, of a hydrostatic pump according to the invention;

FIG. 13 is a detail view showing the connection of two hydrostatic machines at the connecting flanges; and

FIGS. 14 16 are detail views illustrating another aspect of the invention.

SPECIFIC DESCRIPTION In FIG. 1 I have shown a hydrostatic machine having a cubic housing I with surfaces 8 S, and S constituting connecting faces and formed with connecting flanges 2 of circular configuration. The unused flanges 2 are closed by circular cover plate 3. A circular ring may be inserted into the recess fonned by the connecting flange 2 or the latter may be provided with a ridge protruding beyond the face of the connected surface.

The surfaces 8,, S and 8,, respectively opposite the surfaces S through 8;, may, except for surface 5., be identical to the parallel faces. As is also evident from FIG. 1, the faces are of identical dimensions, i.e., each is a square with length and height equal to those of the other surfaces. At the comer of each surface there are provided openings or bores 20 which lie along orthogonal diameters of the circular recess 2 and along diagonals of the respective surfaces. The bores 20 are throughgoing, i.e., extend between and terminate at the opposite surfaces S and S S and S and S and S Hence, tie bolts 8 can be inserted through aligned bores 20 or an assembly of such machines to hold them together as illustrated in FIG. 1.

Also along the orthogonal diameters of the flange 2, there are provided threaded bores 21 into which bolts 22 or may be inserted to secure the cover plate 3 onto the flange or to retain a control or regulating mechanism or device as represented at 23 (see FIG. 10) upon this flange. The flange 2 is formed with a surface bounded by an inner circular wall 2b, the surface 2a lying in a plane close to and parallel to the surface S S in which it is formed. Several or all of the lateral flanges S S S and S may be provided with bores 16, forming a port for the flow of hydraulic fluid to the machine (intake port) or for the flow of fluid out of the machine (discharge port). The plate 3 may be formed with countersinks 23 into which the bolts 22 are recessed so that the exterior of the assembly remains flat even when the cover plates are in place. The cover plates may block the ports 16 as required.

In FIG. 2, I have shown an assembly of two hydrostatic pumps 5 and 6, both of which may be identical to that illustrated in FIG. 1. The shaft 4 of hydrostatic machine 5 extends through the housing and is formed with an internally splined socket 7 communicating with an opening in the rear flange 5a which is exposed when the corresponding cover plate is removed. The splined shaft 4a of the hydrostatic machine 6 is matingly received in the socket 7 so that both pumps are operated together. The hydrostatic machines 5 and 6, therefore, form a double-pump assembly and can also be constituted as a high-pressure distributor for the hydraulic medium. Tie bolts 8 are threaded through the aligned bores 20 (FIG. 1) of the axially aligned machines to hold the two together and bring the flange 6a of the rear machine 6 into sealing contact with the geometrically congruent flange 5a. The machine 6, of course, has the same overall dimensions as the machine 5 and the resulting aggregate has a length twice that of each machine and a width and height equal to that of the individual machines. The lateral face 6b of the pump 6 has its flange closed by a plate 30 affixed to screws 22 which may be countersunk therein as previously noted. The plate 3a is formed with a conduit 12 which thereby registers with the port 16 to provide fluid communication to and from the pump. The port 16 of the flange 2 of face 5b of machine 5 is shown to be exposed.

Another double-pump aggregate has been illustrated in FIG. 3 wherein, however, the large-capacity pump 5 is affixed to a small-capacity pump 9 by tie bolts 10 which are threaded into the bores 21 on the rear flange 5a of the large pump 5. The shaft of pump 9 is received in the socket 7 of pump 5 as previously described. The flanges 9a of the pump 9 are shown to be square but of a geometrically similar configuration to the flanges 5a and 5b of the pump 5. However, the throughgoing bores 20a of these flanges are shown to be located at the vertices of a square of the same dimensions as the square at the comers of which lie the bores 20 of the large pump 5. Hence the flanges 9a, 5a and 5b are geometrically similar, complementary and can be joined in a building-block construction. An inner flange 2d in the form of a recess may be provided as described for the larger hydrostatic machine and may be covered by an appropriate plate affixed by bolts 220 as shown in FIG. 3.

In the embodiment illustrated in FIG. 4, the pump 5 is shown to be affixed to a hydrostatic motor of similar dimensions as represented at 11 by tie bolts 8, the motor shaft being aligned with the shaft 4 of the pump. Hence, the combination of pump and hydrostatic rnotor constitutes an in-line" hydrostatic transmission. The hydraulic connections are provided by conduits 12 on opposite lateral sides of the transmission, terminating in cover plates 13 which are seated in the flange recesses 2 of the hydrostatic pump and motor and are secured by screws 22. A similar in-line transmission is provided in FIG. 5 wherein a smallcapacity hydrostatic motor is connected to the hydrostatic pump 5 by bolts 10 threaded into bores 21 in the rear face 50 of this pump. The output shaft 15 of the transmission is aligned with the input shafi 4 of the pump. Again, hydraulic communication is provided by means of ducts 12a. One end of each duct 12a is fixed in a cover plate 13 received in the flange recess 2 and held in place by screws 22 while the other end of the duct is fixed at its elbow to a geometrically similar cover plate 13a received in a flange recess 2d of the smaller motor 14 and held in place by screws 224 as described with reference to FIG. 3.

FIG. 6 illustrates another compact transmission according to the invention wherein the hydrostatic pump 5 is connected at one of its lateral flanges 5c with the lateral flange 11b of a hydrostatic motor I l of identical dimensions. The transmission is of the Z-drive type wherein the input shaft 4 to the pump and the output shaft 110 of the motor are parallel to one another but are offset by a center-to-center distance equal to the width W of one of the hydrostatic machines. The overall width S of the assembly is 2W while the length" of the compact housing structure is represented at L and is, of course, equal to W. The tie bolts 8, in this embodiment, traverse the bores 20 which run transversely to the shafts. Here again, a duct 12 aflixed to plates 13 serves to make hydraulic connection between the two hydrostatic machines.

FIGS. 7 and 8 illustrate embodiments of hydrostatic transmissions in the form of a drive axle of a motor vehicle. In FIG. 7, the large-capacity pump is driven at its shafi 4 by the internal combustion engine of the vehicle and, in turn, has its hydraulic output connected by a plate 13b and a line 12d to a duct l2e running symmetrically to opposite sides of the pump and communicating via plates 13a with a pair of hydrostatic motors 14, the output shafts 15 of which reach to opposite sides of the vehicle and are connected to the vehicle wheels. Bolts 10 secure the small-capacity hydrostatic motors to the lateral flanges of the pump at the bores 21 thereof. The hydraulic fluid return, on the opposite side of the transmission, not illustrated, can be similar to that shown at 12d and 12s. The stroke volume per revolution of the motors 14 may collectively be equal to that of the pump. The arrangement of FIG. 8, however, provides a pair of hydrostatic motors 11, each of which has a stroke volume per revolution equal to that of the pump. The tie bolts 8a are here used to hold the assembly together and have a length at least equal to 3W In FIG. 9, I have shown an L-drive or right-angle transmission wherein the hydrostatic motor 14 is affixed to one lateral side of the pump 5 by the bolts mentioned previously. The system of FIG. 9 is constructed with the same elements as that of FIG. 5, but whereas the input and output shafts of the latter are coaxial, the coplanar shafls 4 and lie at right angles to one another. In all of the embodiments previously described, unused flange recesses 2 are closed by plates 3.

In FIG. 10, I have shown a Z-drive of the type described in connection with FIG. 6 but wherein the flanges 30 and 31 of the hydrostatic pump 32 and the hydrostatic motor 33, opposite the respective shafts 34 and 35, are provided with control devices 23 and 36 for varying the displacement of the respective hydrostatic machines. The bolts 22 secure these control devices within the recesses 2 of the respective flanges and are threaded into the bores 21 thereof. A modification of the invention is illustrated in FIG. 11 wherein the hydrostatic pump 40 has flanges 41 and 42 inclined at angles 3 of 45 to the flanges 43 and 44 and carrying hydrostatic motors 11 as previously described. The conduits 45 and 46 are attached via plates of the type shown at 13 to the remaining lateral flanges of the pump 40 and to the intake and discharge ports ofthe motor 11. The hydrostatic rrmchine illustrated in FIG. 12 is seen to have a housing 51 of prismatic configuration provided at its lateral faces with connecting flanges as described. The shaft 52 drives a cylinder barrel 53 whose pistons 54 ride against a control plate 55 which is inclined to the axis of the shaft 52 at an angle variable by a control device 23 or 36 not illustrated. The discharge and intake ports 56 and 57 of the barrel communicate via a control plate 58 and suitable pipes with the ports 16 previously described.

In FIG. 13, I have shown an embodiment of the flange coupling of two hydrostatic machines represented generally at 60 and 61. It can be seen that the juxtaposed faces 62 and 63 of the flanges lie in planes P and Pg which are parallel to and close to the planes P and P of the circular recesses 64 and 65 formed in the faces 62 and 63. To center the machines with respect to one another, I prefer to use a ring 66 having a cylindrical outer surface 67 which snugly fits against the inner wall 68 of the recess 65 and is received within the recess 64. The axial height H of this ring is equal at least to twice the depth d of the recesses. The bolts 8 pass through both machines as previously described. When, however, a small-capacity unit is to be affixed to a large-capacity unit, I may provide the small-capacity unit with a ridge which is received in the recess of the large-capacity unit in place of the ring 67. The plate 70 is here shown to lie flush with the surface 63 when the flange of the machine 61 is to be closed and is held in place by the screws 71 which are wholly received in countersinks 72 of the plate.

In FIGS. 15 and 16, I have shown an arrangement wherein the principles of the present invention are applied to the interconnection of machines of different sizes, using a coaxial flange connection. In the arrangement of FIG. 15, for example, the large machine 101 is provided at its connecting flanges with coaxial circular recesses 102 and 202 of large and small diameter, respectively. Any number of such recesses can be provided in steps, depending upon the standard sizes chosen. The small machine 103 has a recess I04 corresponding to the step 202 and may also be stepped if smaller units are to be accommodated. A connecting ring is received in the smaller step 202 and in the step 104 of the two machines and both may be bolted together, e.g., as shown in FIG. 14 or via bolts. In the coupling for the hydrostatic machines of FIG. 15, therefore, each flat face or flange has a recess and the recesses of equal diameter are connected by a ring which projects axially and coaxially from one flange into the other, the faces being substantially flush with one another as already described. In FIG. 16, the coaxial connection is formed by an adapter ring 303 of stepped profile. The large diameter step is snugly received in the large-diameter recess 302 of the larger machine while the smaller step projects axially from the flange face of the larger machine and is received in the smaller diameter coaxial recess 304 of the smaller machine. Here again each of the flanges may be formed with stepped recesses and the rings may be cylindrical, i.e., unstepped.

I claim:

I. A hydrostatic assembly comprising at least two piston-stroke hydrostatic machines, each having a respective shaft rotatable independently of the slmft of the other machine, each of said hydrostatic machines being formed with a respective closed housing having generally planar sides and being closed at all sides to enable independent operation of each machine, the shaft of each of said machines projecting only through one side of the respective housing, means in other sides of each housing forming a fluid inlet and a fluid outlet for the respective machines, said sides of said housings defining geometrically similar confronting flanges, means for detachably securing said machines together with said housin in abutting relationship at said flanges, said flanges being constructed and arranged to enable hydrostatic machines of the same dimensions and configurations and hydrostatic machines of different dimensions and geometrically similar configurations to be affixed to either of the machines in the formation of the assembly, and removable conduit means attached to corresponding sides of said machines for interconnecting the inlets and outlets thereof.

2. The hydrostatic assembly defined in claim 1 wherein each of said housings is prismatic, at least one of said machines being provided within the respective housing with means receiving the projecting shaft of the other machine for coupling of said shafts for joint rotation.

3. The hydrostatic assembly defined in claim 1 wherein each of said machines has a plurality of geometrically identical flanges for interconnection of other machines thereto.

4. The hydrostatic assembly defined in claim 3 wherein at least some of said flanges of each machine lies in planes parallel to the axis of the respective shaft and another of said flanges lies in a plane perpendicular to said axis.

5. The hydrostatic assembly defined in claim 4 wherein at least some of said flanges comprise an outer planar surface formed with a central recess and an inner planar surface set back from said outer recess at the base of said recess, both said surfaces being formed with means for connecting hydrostatic devices to the respective flange.

6. The hydrostatic assembly defined in claim 5, further comprising ports formed within the recesses of at least some of said flanges in the housing of a respective one of said machines and defining said inlets and outlets.

7. The hydrostatic assembly defined in claim 6,

further comprising a cover plate received in one of said recesses for closing the respective port.

8. The hydrostatic assembly defined in claim 6 wherein said conduit means includes at least one plate received in one of said recesses and formed with a duct communicating with the port of the corresponding recess.

9. The hydrostatic assembly defined in claim 8, further comprising means on at least one of said machines for securing a control device externally to the housing thereof.

10. The hydrostatic assembly defined in claim 8 wherein one of said machines is an axial piston pump and another of said machines is an axial piston motor whereby said assembly constitutes a hydraulic transmission.

11. The hydrostatic assembly definai in claim 6 wherein said port is coaxial with said recess.

12. The hydrostatic assembly defined in claim 6 wherein said ports are symmetrically located with respect to the corresponding flanges whereby the machines are interconnectable at said flanges in a plurality of different positions.

13. The hydrostatic assembly defined in claim 3 wherein the interconnected flanges of two such machines are provided with respective coaxial circular is; iz'zsatiyasss szism 13 wherein said recesses are of different diameters and said ring is stepped with corresponding steps of the ring being reclined in the respective recesses.

15. The hydrostatic assembly defined in claim 13 wherein at least one of said recesses is coaxial with at least one further recess of a different diameter adapted to accommodate a ring of a different size on the cor responding flange. 

1. A hydrostatic assembly comprising at least two piston-stroke hydrostatic machines, each having a respective shaft rotatable independently of the shaft of the other machine, each of said hydrostatic machines being formed with a respective closed housing having generally planar sides and being closed at all sides to enable independent operation of each machine, the shaft of each of said machines projectIng only through one side of the respective housing, means in other sides of each housing forming a fluid inlet and a fluid outlet for the respective machines, said sides of said housings defining geometrically similar confronting flanges, means for detachably securing said machines together with said housings in abutting relationship at said flanges, said flanges being constructed and arranged to enable hydrostatic machines of the same dimensions and configurations and hydrostatic machines of different dimensions and geometrically similar configurations to be affixed to either of the machines in the formation of the assembly, and removable conduit means attached to corresponding sides of said machines for interconnecting the inlets and outlets thereof.
 2. The hydrostatic assembly defined in claim 1 wherein each of said housings is prismatic, at least one of said machines being provided within the respective housing with means receiving the projecting shaft of the other machine for coupling of said shafts for joint rotation.
 3. The hydrostatic assembly defined in claim 1 wherein each of said machines has a plurality of geometrically identical flanges for interconnection of other machines thereto.
 4. The hydrostatic assembly defined in claim 3 wherein at least some of said flanges of each machine lies in planes parallel to the axis of the respective shaft and another of said flanges lies in a plane perpendicular to said axis.
 5. The hydrostatic assembly defined in claim 4 wherein at least some of said flanges comprise an outer planar surface formed with a central recess and an inner planar surface set back from said outer recess at the base of said recess, both said surfaces being formed with means for connecting hydrostatic devices to the respective flange.
 6. The hydrostatic assembly defined in claim 5, further comprising ports formed within the recesses of at least some of said flanges in the housing of a respective one of said machines and defining said inlets and outlets.
 7. The hydrostatic assembly defined in claim 6, further comprising a cover plate received in one of said recesses for closing the respective port.
 8. The hydrostatic assembly defined in claim 6 wherein said conduit means includes at least one plate received in one of said recesses and formed with a duct communicating with the port of the corresponding recess.
 9. The hydrostatic assembly defined in claim 8, further comprising means on at least one of said machines for securing a control device externally to the housing thereof.
 10. The hydrostatic assembly defined in claim 8 wherein one of said machines is an axial piston pump and another of said machines is an axial piston motor whereby said assembly constitutes a hydraulic transmission.
 11. The hydrostatic assembly defined in claim 6 wherein said port is coaxial with said recess.
 12. The hydrostatic assembly defined in claim 6 wherein said ports are symmetrically located with respect to the corresponding flanges whereby the machines are interconnectable at said flanges in a plurality of different positions.
 13. The hydrostatic assembly defined in claim 3 wherein the interconnected flanges of two such machines are provided with respective coaxial circular recesses and a ring interconnecting said recesses.
 14. The hydrostatic assembly defined in claim 13 wherein said recesses are of different diameters and said ring is stepped with corresponding steps of the ring being reclined in the respective recesses.
 15. The hydrostatic assembly defined in claim 13 wherein at least one of said recesses is coaxial with at least one further recess of a different diameter adapted to accommodate a ring of a different size on the corresponding flange. 